1. Field of the Invention
The invention relates to a spark plug for an internal combustion engine, especially one which is gas fueled. More specifically, the invention relates to a spark plug with an electrically conducting spark plug body, a central electrode which is located in the spark plug body and which is electrically insulated and projects away from the spark plug body, and a ground electrode which is electrically connected to the spark plug body and which is made in the form of an annular electrode which surrounds the projecting part of the central electrode with an annular ignition gap formed between them.
2. Description of Related Art
A spark plug of the initially mentioned type is known from International Patent Publication WO 91/06142.
The service life requirements for spark plugs for internal combustion engines are increasing considerably at present; this applies especially to spark plugs which are to be used in large-volume, high compression gas-fueled internal combustion engines which are operated in a fixed position. Spark plugs for such a use should have long running time, roughly at least 5000 hours. Since these internal combustion engines operate with high pressure, special importance must be placed on the spark gap. Actually spark gaps of 0.2 to 0.3 mm are nominally set; this means that at a misfire limit of these internal combustion engines of 0.5 to 0.6 mm, according to experience, the potential electrode erosion reserve of 0.2 to 0.3 mm is quickly used up and the misfire limit is quickly reached. Currently available spark plugs do not satisfy the requirement for a long service life; this results in costly replacement of spark plugs.